Surface the immense pressure at the centre of the

Surface Features of The Alpine Fault


New Zealand’s Alpine Fault

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How did it form?

The Earth is composed of four layers (pictured below); the
inner core, outer core, mantle and crust. The inner core, the inner most layer
that makes up the earths centre, is a sphere with a radius of 1,220 km, formed
of mostly an iron-nickel alloy. Although its temperature is estimated to be
close to 5,400 C°, well above iron’s melting point of 1538 C° or
nickel’s 1,455 C°, the inner core is solid, due to the immense pressure at the
centre of the earth keeping the core pressed together. The outer core a sphere
that surrounds the inner core, and is much larger than it at 2,300 km thick. Similarly,
to the inner core, it is mostly made of iron and nickel. The only major
difference between the outer and inner cores is that the outer core is a







The more relevant of earth’s layers to the formation of
fault lines are the mantle and crust. The mantle is the thickest of Earths
layers, at around 2,890 km thick. By far the largest of the Earth’s layers, it
comprises around 84% of the earth, compared to the inner and outer core which
make up 15% of the Earth’s volume. The composition of the mantle varies widely,
with the only real definition of what makes up the mantle as rock. Most of the
rock in the mantle is silicate. Most of this rock is solid, or, closer to the
core, semi liquid, again because of the pressure on the rock solidifying the
rock despite it being over the melting point of most rocks.

During the formation of the earth, earth was constantly
being hit by meteorites that contributed to its size. Because of the heat
generated by the impacts, the earth’s surface was not solid, but rather a magma
ocean. Once the accretion of new meteorites and planetoids by earth’s gravitational
field began to slow, this magma ocean cooled, solidifying into a primordial
crust. Since then, that crust has been changed into a completely different
‘secondary’ crust. The primordial crust was slowly destroyed by erosion, or,
more often, plate tectonics. The crust developed into two separate sections:
oceanic crust and continental crust. Oceanic crust contains more mafic rocks. The
most common of these is basalt, and all mafic rocks are rich in iron and magnesium.
This is as opposed to the rocks more commonly found in the continental crust;
felsic rocks. The most common felsic rock is granite, and felsic rocks are rich
in lighter elements like silicon and oxygen. Because of the relative density of
the oceanic crust, this crust rests lower on the mantle than the continental
crust; therefore, water pools in the basins (which the difference in height
between the types of crust forms) to create oceans.

Although the upper section of the mantle is just as solid as
the crust, it is defined as separate because of the chemical and mineral
differences between the composition of the mantle and the curst. However, for
geological purposes, these two ‘different’ layers are often classed as one
continuous whole; the lithosphere. Underneath the lithosphere is the upper part
of the mantle that, when under pressure, will flow and move rather than break
or deform.

When rock is heated, it expands. This means that warmer rock
is less dense. Therefore, rock from low down in the mantle, where the
temperature is higher, rise as they develop buoyancy as they expand. At the
same time, rocks that have been in higher positions in the mantle slowly sink as
they cool, contract, and gain density. This process creates convection currents
(pictured below), in which there is a constant flow of rock heating, rising,
cooling, falling and heating again. Because all of the rock cannot be moving upwards
and downwards in the same place, convection cells of circular motion are
formed. These slow-moving currents of solid rock not only provides much of the movement
necessary for the plate tectonic process, but also creates the rock cycle.










In the same way that older rock higher in the mantle which have
had more time to cool become denser and sink, so, when the earth was still new,
older, colder sections of the crust slowly sank into the mantle. When this
happened, the surrounding crust was weakened. Over millions of years, this was
repeated enough that the entire lithosphere has fractured into different
pieces. These pieces form the 8 major tectonic plates and the many minor plates.
The lines where plates meet are called fault lines

The entire lithosphere rests on the less rigid, slow-moving
asthenosphere. This means that the tectonic plates slowly move in the direction
that the warmer rock beneath them is moving. Because of this, the way the
convection currents are moving dictates how the tectonic plates move. As shown
in the picture above, the currents are usually the same; they move in circles
going the opposite direction to wherever the upwelling magma is. This means
that at the point where magma rises to the surface, the plates also separate.
This is why volcanoes are common at some fault lines, specifically the ones
where plates are separating, but not fault lines where plates are colliding. At
these fault lines, one plate must dive beneath the other, a process usually
known as subducting. The areas of the lithosphere which are subducting beneath another
plate are known as subduction zones. At fault lines with subduction zones,
often deep trenches are formed, with mountain ranges behind them, caused by the
lowering plate on one side, and the plate on the other side rising above it. Other
fault lines consist of more violent collisions between plates, resulting in the
subduction zone being sheared off of the rest of the plate. This results in the
colliding plates both lifting. This is what is currently happening at the boundary
between the Indian and Asian plates, creating the Himalayas.



There are many more fault lines than tectonic plates, because
fault lines can occur in any place where rock is under stress, and each fault
line is different, but there are broad categories that define faults. Firstly,
faults can be divergent, convergent or transform. Divergent faults are created
where rocks spread apart from each other. When this happens in the Earths
Crust, magma rises from beneath the crust, and usually forms volcanoes. This
creates new crust. To counteract the creation of new crust,

This means that, when viewed with the fault line in a
vertical position, the right-handed plate will move toward the viewer.


The Alpine Fault consists of the meeting between the Pacific
and Australian plates across almost the entire South Island of New Zealand. It
begins slightly off the southwest corner of the South Island, runs along the
West Coast before splitting into several smaller faults in the northeast of the
Island. The Alpine Fault is a right-lateral strike-slip fault (pictured below).
In this case, the right-handed plate is the Pacific Plate, which is moving
south while the Australian Plate moves north. This means that the Southern Alps
move down the west coast at an average rate rate of about 3cm every year. This
movement is not constant, however. The Pacific and Australian Plates are mostly
stuck in place, straining under the pressure of being forced toward and past
each other. When the plates finally move past each other, they violently jump
forward, and cause earthquakes aboveground. These earthquakes happen
approximately once every three hundred years, where the plates move about 10
metres past each other along the alpine fault.

As well as moving across each other, the two plates are also
moving towards each other.  North of the
Alpine Fault the heavier, oceanic Pacific plate is subducting beneath the
Australian Plate. This causes the crust of the Australian Plate to thin out as
it stretches over the Pacific Plate, and this makes it easier for magma to
penetrate the lithosphere. This is the reason for the North Island’s numerous
volcanoes. Along the Alpine Fault the reverse happens, with the Australian
Plate subducting beneath the Pacific Plate. Most of the motion is transform,
with the Pacific Plate moving South by the Australian Plate, however, and the
Australian Plate only subducts beneath the Pacific Plate along the Alpine fault
slowly, especially in comparison to the speed it subducts beneath Fiordland to
the south.










Mt Arthur

Mount Arthur is part of the Arthur Range located in Kahurangi
National Park. The entire region around Mt Arthur, known as the Tablelands. The
tablelands are formed of limestone, while Mt Arthur itself is made almost
entirely out of marble. Mt Arthur is well known for its deep cave systems and the
glacial features near its summit that have formed basins and sinkholes all around
the peak. The Alpine Fault
is about 100 km away from Mt Arthur, but Mt Arthur was still created by it.
(More general Mt Arthur details)







 The reason that Mt
Arthur is mostly marble can be attributed to the internal process known as the
rock cycle. The rock cycle shows how rocks transition between the three main
types of rock; igneous, sedimentary and metamorphic. The most important fact of
the rock cycle is that rock is constantly moving. Over long periods of time,
rock that at one point was on the bottom of the seabed can be pushed lower into
the earth, and then move back up to form mountains. This movement is mainly caused by plate tectonics, in
which subduction zones take rocks down, and seafloor spreading and uplift
produces new rock. Rather than being explained as a continuous cycle, the
rock cycle can be described simply by how each type of rock is created. Sedimentary
rocks are caused by the processes of weathering and erosion. When rocks are
exposed to the atmosphere, small grains, or sediment, are swept off or broken
away from the main body of rock. In most cases, with sedimentary rock, these
grains settle as sand on the seabed (although the same process can happen ono
land, sand is the most common form of eroded grains). These grains are buried
beneath other grains, and undergo lithification, in which the grains are fused
together by pressure, which creates solid rock, known as sedimentary rock. Igneous
rock is created when rocks are pushed beneath the surface to the point that
they become magma. This magma then rises towards the surface in two different
ways; extrusive and intrusive. Extrusive igneous rock rises quickly and is expelled
as lava. It then quickly cools aboveground, into rocks such as obsidian or
basalt. Intrusive igneous rocks rise slower, and cool beneath the surface. This
forms rocks that are less fine-grained, most commonly granite. Metamorphic rock
is changed physically or chemically by high pressure or temperature, usually
deep below ground. The extreme stress often re-crystallises the rock into a
different mineral. An example is graphite changing into diamond under high

-Rock Cycle









Mount Arthur itself is made from marble, which is a metamorphic
rock. Marble is created when carbonate rocks are metamorphized. In the case of
Mount Arthur, and in most cases, the rock marble formed from was limestone. Limestone
itself is a sedimentary rock. Unlike most other sedimentary rocks though,
limestone was not formed from the compressed grains of other eroded rocks.
Limestone is made of calcite grains, which are usually from the skeletons of
marine animals, especially coral. Over millions of years, the grains of coral
and other skeletons that settled onto the seabed near New Zealand compressed and concreted into
limestone. This rock then underwent either high pressure or high temperature
and its grains recrystallized to form marble. This marble uplifted from beneath the
seabed to become a mountain.

-Limestone/Marble Formation

The other major internal process that formed Mount Arthur is
mountain formation.

-Mountain Formation – Folding/Faulting




-Glacial cirques


——How were the caves formed? —–












Franz Josef Glacier


Franz Josef Glacier is located on the West Coast of the
South Island. A glacier is made of snow that has settled and, over time,
solidified into denser ice. Eventually, the ice becomes heavy enough that gravity
slowly drags it downwards. At such a large thickness, rather than acting
brittle as ice usually does, the body of ice flows downwards plastically. Franz
Josef Glacier, specifically, is an alpine glacier. As opposed to a continental
glacier, which covers a large, relatively flat plain and usually empties into
the sea, alpine glaciers travel down valleys in the sides of mountains and end
well above sea level. Franz Josef Glacier itself is 12 km long, and rather than
emptying into a terminal lake, as some glaciers do, the meltwater from the
bottom of the glacier empties as a river.

Glaciers form through a combination of the right meteorological
and geological conditions. Alpine Glaciers are formed from snowfields near the
top of mountains, in which the snowfields do not melt over summer, and so
accumulate over time. Eventually, the snow is packed thick enough that it
starts to solidify into dense ice. This ice builds up and eventually overflows
the area it has formed in. It then slowly moves down the side of the mountain.
If a glacier is formed in a basin or a plateau, it is usually known as an ice
field, often with glaciers flowing out of the overflow points. A glacier is
also separate from an ice cap, which will form anywhere where the climate
conditions are right. They are not bounded by geological features and so will
form over and around mountains.

There are three main conditions needed for glaciers to form.
The first of these is cold temperature. Without extremely cold temperature, snow
will not fall, and any snow that does fall will melt too quickly to form a
glacier. The temperature needed for glacier formation can only be found at high
altitude or latitudes close to the pole. The second condition is consistent snowfall.
Even in areas with cold temperatures, without moisture in the air, snow will
not fall and so glaciers cannot form. The final necessary condition is that
outside factors do not remove the snow. This means that the snowfield must be
sheltered from the wind and not be in an unstable location prone to avalanches.

Franz Josef Glacier travels down from a snow field in the mountains
around Mt Cook. The glacier begins at 2700 metres above sea level and travels
down until it melts at 240 metres above sea level. In the Southern Alps, the
snow line (the height below which snow will melt quickly) varies between 1600
and 2700 metres above sea level. Snow would not have been able to collect without
the height caused by the Southern Alps, which were themselves caused by the
Alpine Fault.

The weather needed for snow to fall is common in New Zealand.
Th climate conditions needed for snow are simply cold temperature (caused by
the height of the Southern Alps) and moisture. In New Zealand, moisture is mostly
brought into the atmosphere by the westerly winds which blow commonly across
the country. These westerly winds, commonly known as the Roaring Forties,
travel around the latitudes between 40 and 50 degrees, uninterrupted except for
Tasmania, New Zealand, and the lower edge of South America. The Southern Alps are
directly exposed to these winds.

-A glacier is

-Franz Josef is this kind of glacier

-details of Franz Josef

-Glaciers are caused by

-Franz Josef was caused by –
what you’re doing now – main point.